3 第三讲 single-row functions. objectives after completing this lesson, you should be able to do...
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3
第三讲
Single-Row Functions
Objectives
After completing this lesson, you should be able to do the following:
• Describe various types of functions availablein SQL
• Use character, number, and date functions in SELECT statements
• Describe the use of conversion functions
SQL Functions
FunctionFunctionInput
arg 1arg 1
arg 2arg 2
arg arg nn
Function performs action
Output
ResultResultvaluevalue
Two Types of SQL Functions
FunctionsFunctions
Single-row Single-row functionsfunctions
Multiple-rowMultiple-rowfunctionsfunctions
Single-Row Functions
Single row functions:
• Manipulate data items
• Accept arguments and return one value
• Act on each row returned
• Return one result per row
• May modify the data type
• Can be nested
• Accept arguments which can be a column or an expression
function_name [(arg1, arg2,...)]function_name [(arg1, arg2,...)]
Single-row Functions
ConversionConversion
CharacterCharacter
NumberNumber
DateDate
GeneralGeneralSingle-row Single-row functionsfunctions
Character Functions
CharacterCharacterfunctionsfunctions
LOWERUPPERINITCAP
CONCATSUBSTRLENGTHINSTRLPAD | RPADTRIMREPLACE
Case-manipulation Case-manipulation functionsfunctions
Character-manipulationCharacter-manipulationfunctionsfunctions
Function Result
Case Manipulation Functions
These functions convert case for character strings.
LOWER('SQL Course')
UPPER('SQL Course')
INITCAP('SQL Course')
sql course
SQL COURSE
Sql Course
Using Case Manipulation Functions
Display the employee number, name, and department number for employee Higgins:
SELECT employee_id, last_name, department_idFROM employeesWHERE last_name = 'higgins';no rows selectedno rows selected
SELECT employee_id, last_name, department_idFROM employeesWHERE last_name = 'higgins';no rows selectedno rows selected
SELECT employee_id, last_name, department_idFROM employeesWHERE LOWER(last_name) = 'higgins';
CONCAT('Hello', 'World')
SUBSTR('HelloWorld',1,5)
LENGTH('HelloWorld')
INSTR('HelloWorld', 'W')
LPAD(salary,10,'*')
RPAD(salary, 10, '*')
TRIM('H' FROM 'HelloWorld')
HelloWorld
Hello
10
6
*****24000
24000*****
elloWorld
Function Result
Character Manipulation Functions
These functions manipulate character strings:
SELECT employee_id, CONCAT(first_name, last_name) NAME, job_id, LENGTH (last_name), INSTR(last_name, 'a') "Contains 'a'?"FROM employeesWHERE SUBSTR(job_id, 4) = 'REP';
Using the Character Manipulation Functions
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2
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3
Number Functions
• ROUND: Rounds value to specified decimalROUND(45.926, 2)
45.93
• TRUNC: Truncates value to specified decimalTRUNC(45.926, 2)
45.92
• MOD: Returns remainder of divisionMOD(1600, 300)
100
SELECT ROUND(45.923,2), ROUND(45.923,0), ROUND(45.923,-1)FROM DUAL;
Using the ROUND Function
DUAL is a dummy table you can use to view results from functions and calculations.
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3
31 2
SELECT TRUNC(45.923,2), TRUNC(45.923), TRUNC(45.923,-2)FROM DUAL;
Using the TRUNC Function
31 2
1 2
3
SELECT last_name, salary, MOD(salary, 5000)FROM employeesWHERE job_id = 'SA_REP';
Using the MOD Function
Calculate the remainder of a salary after it is divided by 5000 for all employees whose job title is sales representative.
Working with Dates
• Oracle database stores dates in an internal numeric format: century, year, month, day, hours, minutes, seconds.
• The default date display format is DD-MON-RR.– Allows you to store 21st century dates in the 20th century by
specifying only the last two digits of the year.
– Allows you to store 20th century dates in the 21st century in the same way.
SELECT last_name, hire_dateFROM employeesWHERE last_name like ''G%';';
Working with Dates
SYSDATE is a function that returns:
• Date
• Time
Arithmetic with Dates
• Add or subtract a number to or from a date for a resultant date value.
• Subtract two dates to find the number of days between those dates.
• Add hours to a date by dividing the number of hours by 24.
Using Arithmetic Operatorswith Dates
SELECT last_name, (SYSDATE-hire_date)/7 AS WEEKSFROM employeesWHERE department_id = 90;
Date Functions
Number of monthsbetween two dates
MONTHS_BETWEEN
ADD_MONTHS
NEXT_DAY
LAST_DAY
ROUND
TRUNC
Add calendar months to date
Next day of the date specified
Last day of the month
Round date
Truncate date
Function Description
• MONTHS_BETWEEN ('01-SEP-95','11-JAN-94')
Using Date Functions
• ADD_MONTHS ('11-JAN-94',6)
• NEXT_DAY ('01-SEP-95','FRIDAY')
• LAST_DAY('01-FEB-95')
19.6774194
'11-JUL-94'
'08-SEP-95'
'28-FEB-95'
• ROUND(SYSDATE,'MONTH') 01-AUG-95
• ROUND(SYSDATE ,'YEAR') 01-JAN-96
• TRUNC(SYSDATE ,'MONTH') 01-JUL-95
• TRUNC(SYSDATE ,'YEAR') 01-JAN-95
Using Date Functions
Assume SYSDATE = '25-JUL-95':
Conversion Functions
Implicit data typeImplicit data typeconversionconversion
Explicit data typeExplicit data typeconversionconversion
Data typeData typeconversionconversion
Implicit Data Type Conversion
For assignments, the Oracle server can automaticallyconvert the following:
VARCHAR2 or CHAR
From To
VARCHAR2 or CHAR
NUMBER
DATE
NUMBER
DATE
VARCHAR2
VARCHAR2
Implicit Data Type Conversion
For expression evaluation, the Oracle Server can automatically convert the following:
VARCHAR2 or CHAR
From To
VARCHAR2 or CHAR
NUMBER
DATE
Explicit Data Type Conversion
NUMBERCHARACTER
TO_CHAR
TO_NUMBER
DATE
TO_CHAR
TO_DATE
Using the TO_CHAR Function with Dates
The format model:
• Must be enclosed in single quotation marks and is case sensitive
• Can include any valid date format element
• Has an fm element to remove padded blanks or suppress leading zeros
• Is separated from the date value by a comma
TO_CHAR(date, 'format_model')TO_CHAR(date, 'format_model')
YYYY
Elements of the Date Format Model
YEAR
MM
MONTH
DY
DAY
Full year in numbers
Year spelled out
Two-digit value for month
Three-letter abbreviation of the day of the week
Full name of the day of the week
Full name of the month
MONThree-letter abbreviation of the month
DD Numeric day of the month
Using the TO_CHAR Function with Numbers
These are some of the format elements you can use with the TO_CHAR function to display a number value as a character:
TO_CHAR(number, 'format_model')TO_CHAR(number, 'format_model')
9
0
$
L
.
,
Represents a number
Forces a zero to be displayed
Places a floating dollar sign
Uses the floating local currency symbol
Prints a decimal point
Prints a thousand indicator
SELECT TO_CHAR(salary, '$99,999.00') SALARYFROM employeesWHERE last_name = 'Ernst';
Using the TO_CHAR Function with Numbers
Using the TO_NUMBER and TO_DATE Functions
• Convert a character string to a number format using the TO_NUMBER function:
• Convert a character string to a date format using the TO_DATE function:
• These functions have an fx modifier. This modifier specifies the exact matching for the character argument and date format model of a TO_DATE function
TO_NUMBER(char[, 'format_model'])TO_NUMBER(char[, 'format_model'])
TO_DATE(char[, 'format_model'])TO_DATE(char[, 'format_model'])
RR Date Format
Current Year1995199520012001
Specified Date27-OCT-9527-OCT-1727-OCT-1727-OCT-95
RR Format1995201720171995
YY Format1995191720172095
If two digits of the current year are:
0–49
0–49 50–99
50–99
The return date is in the current century
The return date is in the century after the current one
The return date is in the century before the current oneThe return date is in the current century
If the specified two-digit year is:
Example of RR Date Format
To find employees hired prior to 1990, use the RR format, which produces the same results whether the command is run in 1999 or now:
SELECT last_name, TO_CHAR(hire_date, 'DD-Mon-YYYY')FROM employeesWHERE hire_date < TO_DATE('01-Jan-90', 'DD-Mon-RR');
Nesting Functions
• Single-row functions can be nested to any level.
• Nested functions are evaluated from deepest level to the least deep level.
F3(F2(F1(col,arg1),arg2),arg3)
Step 1 = Result 1
Step 2 = Result 2
Step 3 = Result 3
SELECT last_name, NVL(TO_CHAR(manager_id), 'No Manager')FROM employeesWHERE manager_id IS NULL;
Nesting Functions
General Functions
These functions work with any data type and pertainto using nulls.• NVL (expr1, expr2)• NVL2 (expr1, expr2, expr3)• NULLIF (expr1, expr2)• COALESCE (expr1, expr2, ..., exprn)
NVL Function
Converts a null to an actual value.
• Data types that can be used are date, character, and number.
• Data types must match:– NVL(commission_pct,0)– NVL(hire_date,'01-JAN-97')– NVL(job_id,'No Job Yet')
SELECT last_name, salary, NVL(commission_pct, 0), (salary*12) + (salary*12*NVL(commission_pct, 0)) AN_SALFROM employees;
Using the NVL Function
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12
SELECT last_name, salary, commission_pct, NVL2(commission_pct, 'SAL+COMM', 'SAL') incomeFROM employees WHERE department_id IN (50, 80);
Using the NVL2 Function
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Conditional Expressions
• Provide the use of IF-THEN-ELSE logic within a SQL statement
• Use two methods:– CASE expression– DECODE function
The CASE Expression
Facilitates conditional inquiries by doing the work of an IF-THEN-ELSE statement:
CASE expr WHEN comparison_expr1 THEN return_expr1 [WHEN comparison_expr2 THEN return_expr2 WHEN comparison_exprn THEN return_exprn ELSE else_expr]END
CASE expr WHEN comparison_expr1 THEN return_expr1 [WHEN comparison_expr2 THEN return_expr2 WHEN comparison_exprn THEN return_exprn ELSE else_expr]END
SELECT last_name, job_id, salary, CASE job_id WHEN 'IT_PROG' THEN 1.10*salary WHEN 'ST_CLERK' THEN 1.15*salary WHEN 'SA_REP' THEN 1.20*salary ELSE salary END "REVISED_SALARY"FROM employees;
Using the CASE Expression
Facilitates conditional inquiries by doing the work of an IF-THEN-ELSE statement:
…
…
The DECODE Function
Facilitates conditional inquiries by doing the work of a CASE or IF-THEN-ELSE statement:
DECODE(col|expression, search1, result1 [, search2, result2,...,] [, default])
DECODE(col|expression, search1, result1 [, search2, result2,...,] [, default])
Using the DECODE Function
SELECT last_name, job_id, salary, DECODE(job_id, 'IT_PROG', 1.10*salary, 'ST_CLERK', 1.15*salary, 'SA_REP', 1.20*salary, salary) REVISED_SALARYFROM employees;
…
…
Using the DECODE Function
SELECT last_name, salary, DECODE (TRUNC(salary/2000, 0), 0, 0.00, 1, 0.09, 2, 0.20, 3, 0.30, 4, 0.40, 5, 0.42, 6, 0.44, 0.45) TAX_RATEFROM employeesWHERE department_id = 80;
Display the applicable tax rate for each employee in department 80.
Summary
In this lesson, you should have learned how to: • Perform calculations on data using functions
• Modify individual data items using functions
• Manipulate output for groups of rows using functions
• Alter date formats for display using functions
• Convert column data types using functions
• Use NVL functions
• Use IF-THEN-ELSE logic
Practice 3 Overview
This practice covers the following topics:
• Writing a query that displays the current date
• Creating queries that require the use of numeric,character, and date functions
• Performing calculations of years and months of service for an employee
Practice 3 Overview
• Creating queries that require the use of numeric, character, and date functions
• Using concatenation with functions
• Writing case-insensitive queries to test the usefulness of character functions
• Performing calculations of years and months of service for an employee
• Determining the review date for an employee
Practice 3
Practice 3